Electrically powered outdoor lighting systems are used to illuminate pathways, yards, parks and other like areas. Commonly, such lights are connected to public utility systems, or similar sources of electrical power and are controlled by preset timing devices, to illuminate desired areas at nightfall and automatically turn off at a predetermined time, for example, prior to daybreak.
Many conventional lighting devices require extensive cabling, suitable timing mechanisms and the like, and are thus relatively expensive to install and maintain. In addition, such lighting devices utilize electric power generated in a conventional manner such as by burning fossil fuels. Burning of fossil fuels contributes to contamination of the environment and depletion of existing fuel resources.
Lighting devices which utilize solar energy and do not operate off a public utility source of power or the like, have proved to be a viable and desirable alternative. Solar lighting devices are desirable because they are relatively inexpensive and require hardly any maintenance.
Existing solar lighting devices have a self-contained electrical storage device which is maintained in a charged condition by a solar cell array. The solar cell array provides current at a required voltage to charge an electrical storage device during the day. Illumination is provided by supplying charge from an electrical storage device to an electrical light source such as a light bulb at night when the solar cell array is not producing electricity. The charging current supplied to the electrical storage device is controlled by the sunlight intensity and the size and efficiency of the solar cell array. Such solar lighting devices, although known to perform satisfactorily at normal temperatures, deteriorate in performance at elevated temperatures.
Generally, such solar lighting devices include electrical storage devices which function at their optimum at a specified operating temperature. At this temperature, the electrical storage device accepts all of the charge produced by the solar cell array. Commonly, in such devices, the electrical storage device is disposed in close proximity to the solar cell array to allow charge to be easily and efficiently transferred from the solar cell array to the electrical storage device. In such an arrangement, since the electrical storage device is in heat transfer proximity to the solar cell array, heat generated by the solar cell array causes the electrical storage device to become undesirably hot, thus, elevating its temperature beyond the operating temperature specified by the manufacturer. At temperatures higher than the operating temperature, the charge acceptance capabilities of the electrical storage device decrease substantially. This is undesirable because sunlight to power the solar cell array is available only during a relatively short period of time each day. The current level generated by the solar cell array when in excess of the charge acceptance of the electrical storage device causes it to overheat and sustain damage, thereby causing the overall performance of the solar powered lamp to deteriorate.
In one approach to overcome this problem, the electrical storage device may be arranged remote from the solar cell array. Although this prevents the electrical storage device from absorbing heat generated by the solar cell array, thus, maintaining the operating temperature at a normal level in hot weather, it is not satisfactory during cold weather because the electrical storage device is unable to provide current sufficient to illuminate the bulb at temperatures below its operating temperature. The electrical storage device is therefore typically placed in heat transfer proximity to the solar cell array so that heat absorbed by the solar cell array on a sunny day helps elevate the temperature of the power source to its normal operating temperature even if the ambient temperature is low.
Moreover, existing solar lighting devices are configured in a manner which does not provide for the flow of air through the lamp. This further contributes to higher temperatures and inefficient performance at such temperatures.
Prior configurations of solar lighting devices comprise a plurality of parts which are held together In an arrangement such that they are easily dislodged during use and are difficult and time-consuming to reassemble or repair.
A need thus exists for a solar powered lamp which functions more efficiently at elevated temperatures. A need also exists for a solar powered lamp which can be assembled securely and disassembled with ease.